Switched capacitor circuit modifying voltage on the inductor of a buck regulator

ABSTRACT

A voltage regulator provides a regulated output voltage [ 108]  from an input voltage [ 100]  using control unit [ 106]  to control a switched capacitor circuit [ 102]  to periodically produce different output voltage levels Vx followed by a low pass filter [ 104]  to give a regulated output voltage. Phase interleaving is used where the phases of different voltage levels are interleaved allowing for increased effective switching frequency and reduced switching losses. By controlling the average voltage on the flying capacitors, output voltage is regulated by modulating the resistance of the switches using a duty cycle. A control unit [ 106]  is used to determine the operation region of the voltage regulator device and configure the switched capacitor circuit in each operation region. The controller contains a state machine that determines the switches configuration in each phase of a complete switching cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/US2015/015696 filed on Feb. 12, 2015.PCT/US2015/015696 filed on Feb. 12, 2015 claims the benefit of U.S.Provisional Application 61/940,337 filed on Feb. 14, 2014

FIELD OF THE INVENTION

The present invention relates generally to voltage regulator devices(also known as DC-DC converters) and methods for operating them. Moreparticularly, the invention relates to DC-DC converters capable ofproviding step-up, step-down or step-up/down conversions.

BACKGROUND OF THE INVENTION

Modern microprocessors have many cores integrated on one chip. Each coreis preferred to operate at a different supply voltage domain to supportthe dynamic voltage and frequency scaling feature. This means each corerequires a separate voltage regulator that has high efficiency over awide range of output voltage levels. Integration of high efficiencyvoltage regulators on chip is a challenge.

While normal switched capacitor voltage regulators (SCVRs) are easyintegrable, they are suffering from charge sharing losses as well asfast degradation of efficiency when deviating from the target operationpoint. On the other hand, conventional buck converters suffer from largemagnetic components that introduce challenges to integrate on chip. Avoltage regulator device that has the advantages of both the SCVR andthe buck converters would be a needed improvement in the art.

SUMMARY OF THE INVENTION

In one aspect, embodiments of the invention include a voltage regulatorhaving a switched capacitor circuit (SCC) capable of switching itsoutput voltage periodically between two or more voltage levels, thusproviding a smaller voltage drop on the inductor. The voltage regulatordevices include a switched capacitor circuit (e.g., using flyingcapacitors) that takes an input voltage and is capable of providingdifferent voltage levels. The switched capacitor circuit is followed bya low pass filter to give a regulated output voltage. The switchedcapacitor circuit is configured to switch its output periodicallybetween several different voltage levels (e.g., adjacent levels)allowing for smaller inductor sizes and smaller capacitor sizes withoutdegrading the performance. The device can be used for DC-DC powerconversion both on-chip and off-chip, and used to provide a regulated DCoutput voltage to power electronic circuits. In one embodiment, theinvention is capable of providing three types of voltage conversion thatinclude step-up, step down and step-up/down conversions.

In a further aspect, embodiments of the invention include methods foroperating voltage regulators using a phase interleaving technique wherea complete switching cycle is divided into a predetermined number oftime slots, e.g., double the maximum number of phases, providing anyvoltage level of the SCC. Each time slot is assigned one of the phasesof two or more different conversion ratios. Given a certain desiredoutput voltage range, some phase sequences lead to a reduced number ofswitching MOSFETs during a complete switching cycle which in turn reduceswitching losses. In addition, some phase sequences lead to lower stresson switching capacitors allowing for smaller capacitor sizes and lesscharge sharing losses. Preferable conditions and constraints for properoperation of the circuit under this method are also provided.Interleaving the phases of different voltage levels increases theeffective switching frequency of the circuit and reduces switchinglosses.

Embodiments of the invention also include methods for controlling theaverage voltage on the flying capacitors to balance a flying capacitorin a multilevel multistate voltage regulator. This method allows forregulating the output voltage by modulating the resistance of theswitches using a duty cycle. The average voltage on the flying capacitorbecomes dependent on the duty cycle of the switches driving waveformsdue to the existence of an inductor in the path from the input to theoutput. This allows the flying capacitor to deviate from its normalbalance values. As a result of that, a voltage waveform of two differentvoltage levels is generated at the input of the inductor. The low passfilter following the switched capacitor circuit takes the average ofthis voltage waveform generating a regulated output voltage. As the dutycycle changes, the average voltage on the flying capacitor changes andso does the output voltage. The dependency of the flying capacitorvoltage on the duty cycle increases as the inductor size increases. Thisallows for a wider range of accessible output voltage values while theduty cycle goes from minimum to maximum. There is a certain duty cyclevalue which gives the maximum output voltage, the maximum efficiency andthe minimum output voltage ripples. Specifically, for a 2:1 topologyused as an example, the duty cycle value is 0.5 and the correspondingmaximum output voltage is 0.5 Vin.

Embodiments of the invention include a controller for operating thevoltage regulator device. A controller structure has switchconfigurations for the switched capacitor circuit. The operationtimeline of the switched capacitor circuit is divided into phases eachwith its duration. Power conversion is done by charging/dischargingstorage elements like capacitors and inductors. A control unit is usedto determine the operation region of the voltage regulator device andconfigure the switched capacitor circuit in each operation region. Thecontroller contains a state machine that determines the switchesconfiguration in each phase of a complete switching cycle.

Advantageously, embodiments of the invention fills the gap betweeninductor-based voltage regulators and capacitor-based voltageregulators. While each type of these voltage regulators has itsadvantages and disadvantages, the voltage regulator according toembodiments of the current invention takes the advantages of bothregulator types, while avoiding or minimizing their disadvantages. Thevoltage regulator according to one embodiment is a general structurewhere many specific voltage regulators targeting different applicationscan be built based on the principles of the general structure. In oneaspect, the voltage regulator is assigned with a controlling techniquethat helps in a further boost of its performance that can be consideredas an optimum solution for challenges and requirements of modern voltageregulators.

Advantageously, embodiments of the voltage regulator have small passivecomponents, making it an integrable on-chip device that consumes lessarea off-chip. These aspects enable electronic devices with smallersize. For modern processors, the trend is to increase the number ofcores on the chip, where each core needs a separate voltage regulator tosupport the dynamic voltage and frequency-scaling feature. Embodimentsof the current invention provide a regulator that is integrable on chipand with high efficiency.

Some exemplary applications of the invention include energy harvestingsystems (e.g., solar energy harvesting for wireless sensor networks),on-chip power management (e.g. multi-core processors), off-chip powermanagement for electronic systems, and power management forSystem-on-Chips (SoCs). Applications also include high powerapplications like solar energy systems for homes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bock diagram of a multilevel multistate voltage regulatordevice according to an embodiment of the invention.

FIG. 2 is a graph of voltage vs. time illustrating a switching voltagewaveform Vx generated at the output of the switched capacitor circuit ofFIG. 1.

FIG. 3 is an illustration of a working principle of the multilevelmultistate voltage regulator device of FIG. 1.

FIG. 4A is a graph of voltage vs. time illustrating a voltage waveformgenerated at the output of the switched capacitor circuit of FIG. 1.

FIG. 4B is a timeline illustrating a phase interleaving method betweentwo conversion ratios, according to an embodiment of the invention.

FIG. 5 is a flow diagram illustrating the inter-relationships betweenvarious operating conditions and constraints, according to an embodimentof the invention.

FIGS. 6A-B show first and second phases of the voltage regulatoroperation in which the flying capacitor is charging and discharging,according to an embodiment of the invention.

FIGS. 7A-B show the equivalent models of the circuits in FIG. 6A-B,respectively.

FIG. 8A is a graph of average voltage on the flying capacitor (Vf) andthe output voltage (Vout) versus the duty cycle, corresponding to thecircuits shown in FIGS. 6A-B.

FIG. 8B is a graph of average voltage on the flying capacitor versus theduty cycle of the waveforms controlling the switches for differentvalues of inductor size, according to an embodiment of the invention.

FIG. 9 is a schematic circuit diagram illustrating an example of a4-level 4-state voltage regulator device, according to an embodiment ofthe invention.

FIG. 10 is a table illustrating three different operation regions of the4-level 4-state voltage regulator device of FIG. 9.

FIG. 11 is a table illustrating the different operation regions of aconventional triple-ratio SCC known in the art.

FIGS. 12A-C are timing diagrams showing different configurations of aswitched capacitor circuit and the resulting voltage waveform in thefirst, second, and third operation regions of the 4-level 4-statevoltage regulator of FIG. 9.

FIG. 13 is a graph of efficiency vs. output voltage showing a comparisonbetween the 4-level 4-state voltage regulator of FIG. 9 and aconventional triple-ratio resonant switched capacitor regulator.

FIG. 14 is a graph of output ripples vs. output voltage showing acomparison between 4-level 4-state voltage regulator of FIG. 9 and aconventional triple-ratio resonant switched capacitor regulator.

FIG. 15 is schematic circuit diagram of a 5-level 8-state voltageregulator device, according to an embodiment of the invention.

FIG. 16 is a table illustrating the different operation regions of the5-level 8-state voltage regulator device of FIG. 15.

FIG. 17A is a graph of the voltage on the flying capacitors vs. time forthe circuit of FIG. 15.

FIG. 17B is graph of the voltage Vout at the device output node vs. time(top) and the voltage Vx at the SCC switching output node vs. time(bottom), for the 5-level 8-state voltage regulator circuit shown inFIG. 15.

FIG. 18 is a schematic circuit diagram illustrating the structure of acontroller unit and its working principle, according to an embodiment ofthe invention.

DETAILED DESCRIPTION

A multilevel multistate voltage regulator design according to principlesof the present invention is described in detail below with references toFIGS. 1-3. This design uses a switched capacitor circuit (SCC) to switchbetween different levels in different phase and the use of an inductorand the use of a duty cycle control with switch cap to get arbitraryoutput voltage. In the general case, the SCC switches its output betweenany number of voltage levels periodically. In one example, the SCC isswitching its output periodically between two voltage levels. A methodfor operating DC-DC converters by phase interleaving technique is alsodescribed below in relation to FIGS. 4-5. This method for interleavingphases and clocks reduces power consumption. In general, the phases ofany number of voltage levels may be interleaved. In one example, thephases of two voltage levels are interleaved. A method to operate DC-DCconverters by resistance modulation of switches using a duty cycle isalso described below in relation to FIGS. 6-8. This switch resistancemodulation method uses the duty cycle to regulate the output of thevoltage regulator. An illustrative embodiment of a 4-level 4-statevoltage regulator implementing the general principles of a multilevelmultistate voltage regulator device and phase interleaving technique isdescribed below in relation to FIGS. 9-14. Another such illustrativeembodiment of a 5-level 8-state voltage regulator implementing thegeneral multilevel multistate voltage regulator device and phaseinterleaving is described in relation to FIGS. 15-17, and a digitalcontroller for this illustrative voltage regulator device is describedbelow in relation to FIG. 18.

FIG. 1 shows a high-level block diagram of a multilevel multistatevoltage regulator device according to an embodiment of the invention.The device includes three main blocks: a switched capacitor circuit(SCC) 102, a low pass filter (LPF) 104 and a controller 106. Block 102is a multi-ratio switched capacitor circuit (SCC) that is capable ofdelivering two or more different output voltage levels V1, V2, . . . ,Vn from an input voltage Vin 100. The switched capacitor circuit (SCC)102 is periodically switching its output between different voltagelevels V1, V2, . . . , Vn, generating a switching voltage waveform Vx atits output. The block 104 is a low pass filter that takes the average ofthe voltage waveform Vx at its input and provides a regulated outputvoltage Vout 108. Block 104 includes an inductor (L) followed by anoutput capacitor (decoupling capacitor). Block 106 is a controller thatis responsible for generating the different configurations for the SCCalong the operation timeline of the voltage regulator. The controllertakes the output voltage Vout 108 and the target reference voltage Vref110 (representing the desired output voltage) as an input and generatesswitch driving waveforms 112 as an output. This device provides a highroughly-constant efficiency (i.e., between 70% and 90%) over most of theoperation range with low output ripples (i.e., lower than 30 mV) withrespect to other devices in the art. This aspect helps in saving thepower consumption of the electronic device in different operation modes,such as sleep mode.

The SCC 102 includes a combination of switches and flying capacitors.Each of the voltage levels V1, V2, . . . , Vn is produced by a certainconversion ratio where each conversion ratio corresponds to certainphases (i.e., configurations for the SCC) to provide this voltage level.The voltage levels that the SCC produces may include the two powersupply rails (i.e., Vin and Ground) which may be provided by a directconnection between input and output nodes of the SCC without any flyingcapacitors involved in the charge transferring process.

The LC Low Pass Filter (LPF) 104 includes an inductor (L) and adecoupling output capacitor (Co) of the voltage regulator. Thedecoupling output capacitor works on reducing the output voltageripples. The low pass filter block 104 does not have any regulationcapability (i.e., no switches); it just takes the average of theswitching voltage waveform generated at its input.

The voltage regulator device of FIG. 1 can be used to build step-up,step-down or step up/down DC-DC converters. For a step-up converter, thevoltage levels the SCC produces are higher than or equal to the inputvoltage. In a step-down converter, the SCC produces voltage levels lowerthan or equal to the input voltage where the highest voltage level isconsidered to be the input voltage and the lowest voltage level isconsidered to be the ground. In a step-up/down converter, some voltagelevels are higher than the input voltage and some are lower.

FIG. 2 is an example graph of voltage vs. time illustrating a switchingvoltage waveform Vx generated at the output of the switched capacitorcircuit of FIG. 1 resulting from periodically switching the outputvoltage level between four different voltage levels V1, V2, V3, V4,according to an embodiment of the invention. The voltage levels V1, V2,V3 and V4 are produced with durations of tv1, tv2, tv3, and tv4,respectively, as configured through the controller. The sum of tv1, tv2,tv3 and tv4 is equal to one switching period (Tsw). The durations tv1,tv2, tv3, and tv4 are adjusted such that the average of the switchingvoltage waveform Vx is equal to the desired output voltage (Vout) asfollows:V1(Tv1/Tsw)+V2(Tv2/Tsw)+V3(Tv3/Tsw)+V4(Tv4/Tsw)=VoutThe LPF takes the average of the switching voltage waveform, producingthe regulated desired output voltage Vout.

FIG. 3 is an illustration for the working principle of the multilevelmultistate voltage regulator device of FIG. 1, showing differentoperation regions of the regulator, according to an embodiment of theinvention. In this illustrated example, the SCC is configured to switchits output voltage between two adjacent voltage levels periodically.Accordingly, for a SCC capable of providing n voltage levels that mayinclude the two power supply rails, there are (n−1) different operationregions the regulator can be configured to work at. In the firstoperation region (OP1), the SCC is configured to change its outputvoltage between V1 and V2 periodically. In the Second operation region(OP2), the SCC is configured to change its output voltage periodicallybetween V2 and V3 voltage levels, and so on. In the last operationregion (OPn−1), the SCC is configured to change its output voltage levelperiodically between Vn−1 and Vn voltage levels. In each of the (n−1)operation regions, the desired output voltage of the regulator (Vout)lies between the two voltage levels of that operation region. Therefore,the selection of the desired operation region is considered a coarsetuning of the output voltage, as illustrated in the central column ofthe figure. The switching voltage waveform (Vx) produced by the SCC ineach operation region is averaged by passing through the LPF, resultingin a regulated output voltage (Vout). As shown in the right column ofthe figure, fine tuning of the output voltage value inside eachoperation region may be performed through the adjustment of a duty cyclevalue (D) which controls the relative duration between the two voltagelevels of each operation region.

When the SCC is configured to switch its output periodically between twoadjacent voltage levels where the desired output voltage lies inbetween, the maximum voltage drop on the inductor of the LPF is reduced.This may result in a reduction in the peak-to-peak current ripples inthe inductor which, in this case, would be given byΔIL=[(V2−V1)D(1−D)]/[L·Fsw], where V1, V2 are the two voltage levelsbetween which the SCC is configured to switch, D is the duty cycle whichrepresents the relative duration between the duration of the highervoltage level with respect to the switching period (Tsw), and L is theinductor size of the LPF. The reduction in the peak-to-peak currentripples in the inductor results in reduced conduction losses of theregulator and can result in a reduction of the inductor size used in theLPF.

FIGS. 4A-B illustrate aspects of applying the phase interleavingtechnique to the voltage regulator device in FIG. 1 when the SCC isconfigured to switch its output periodically between two adjacentvoltage levels V1 and V2. Under the phase interleaving technique, theoperation timeline of the regulator has several switching cyclesrepeated as long as the circuit stays in some operation region. Oneswitching cycle has a duration period (Tsw) equal to one over the mainswitching frequency of the regulator (Fsw) and is divided into a numberof time lots (or states) where each state is assigned to a certain phasefrom the SCC. Each time slot (or state) has its relative duration to themain switching cycle duration (Tsw).

FIG. 4A is a graph of voltage vs. time illustrating the voltage waveformgenerated at the output of the switched capacitor circuit of FIG. 1,illustrating a case where the SCC is switching between two adjacentvoltage levels (V1 and V2), resulting from interleaving betweendifferent phases of two conversion ratios, according to an embodiment ofthe invention. FIG. 4B is a timeline illustrating a phase interleavingmethod between two conversion ratios, according to an embodiment of theinvention.

For the case where the SCC is configured to switch between two voltagelevels V1 and V2 periodically as shown in FIG. 4A, the operationtimeline of the regulator is divided into 2n time slots where nrepresents the maximum number of phases required to provide either V1 orV2, as indicated in FIG. 4B. The odd time slots of the switching cycleare assigned to phases providing the first voltage level V1 while theeven time slots of the switching cycle are assigned to phases providingthe second voltage level V2. The summation of the odd time slots (T1,T3, . . . , T2 n−1) is equal to the total duration of the first voltagelevel V1 inside a one switching cycle and is given by T1+T3+ . . . +T2n−1=DTsw, where D is the duty cycle representing the relative durationof the first voltage level to the duration of one switching cycle (Tsw).The summation of the even time slots (T2, T4, . . . , T2 n) is equal tothe total duration of the second voltage level inside a one switchingcycle and is given by T2+T4+ . . . +T2 n=(1−D)Tsw. If one voltage levelis provided by a number of phases higher than that of the other voltagelevel, some of the phases of the other voltage levels are repeated inthe switching cycle until the total number of phases providing eachvoltage level are equal.

FIG. 5 is a flow diagram illustrating the inter-relationships betweenvarious operating conditions and constraints, according to an embodimentof the invention. The figure provides guidelines 400, 402, 404, 406,408, 410 for selecting a proper SCC topology for the voltage regulatordevice in FIG. 1 and assigning the phases of its different voltagelevels to different timeslots of the switching cycle. It should be notedthat the SCC topology in FIG. 1 may be selected from one of the switchedcapacitor circuit topologies known in the art (e.g., Series-Paralleltopology, Ladder topology, Dickson topology, etc.), provided itsatisfies appropriate conditions, as illustrated in FIG. 5. The phasesof different voltage levels of the SCC topology are assigned to theswitching cycle in a way that keeps the flying capacitor balanced attheir target values by following the guidelines mentioned in FIG. 5.

FIGS. 6A and 6B are schematic circuits that illustrate a technique forcontrolling the output voltage of a voltage regulator device through theresistance modulation of switches by controlling the flying capacitoraverage voltage in the two phases of a 2:1 conversion ratio, accordingto an embodiment of the invention. The circuit includes four MOSFETswitches: S1, S2, S3 and S4 and one flying capacitor (Cf) constitutingthe conventional 2:1 switched capacitor circuit known in the art. Theswitched capacitor circuit is followed by a low pass filter including aninductor (L) and an output capacitor (Co). Vin is the input voltage tothe regulator and Vout is the output voltage while Io represents theoutput current drawn by the load circuit. In the conventional 2:1switched capacitor converter without an inductor, the flying capacitoris normally balanced at half the input voltage during normal operationof the circuit. The existence of an inductor (L) between the flyingcapacitor (Cf) and the output capacitor (Co) in the voltage regulatordevice shown in FIGS. 6A-B allows the voltage on the flying capacitor(Cf) to deviate from the normal value (i.e., 0.5 Vin) as the inductorcan support arbitrary voltage drops on it.

FIG. 6A shows the first phase of the voltage regulator operation inwhich the flying capacitor (Cf) is charging through the input source. Inthis case, the two MOSFET switches S1 and S3 are turned on by biasingthem at a constant driving voltage (Vd). Switches S2 and S4 are turnedoff, as indicated by dashed lines. FIG. 6B shows the second phase of thevoltage regulator operation in which the flying capacitor (Cf) isdischarging through the inductor (L). In this case, the two MOSFETswitches S2 and S4 are turned on by biasing them at a constant drivingvoltage (Vd). Switches S1 and S3 are turned off, as indicated by dashedlines.

FIGS. 7A-B show the equivalent model of the circuits in FIG. 6A-B,respectively. Controlling the on-resistance of the MOSFET through theduty cycle controls the voltage drop exhibited on the MOSFET and hencethe output voltage (Vout). FIGS. 7A and 7B are schematic circuits thatillustrate a model of two phases 2:1 switched capacitor circuit withresistance modulation, according to an embodiment of the invention.R=f(Vf) represents the on-resistance of the switch which is a functionof the voltage on the flying capacitor (Vf). As the flying capacitorvoltage changes, the on-resistance of the MOSFET increases or decreasesaccording to the position of that MOSFET in the circuit. Cf is theflying capacitor, Co is the output capacitor, L is the inductor, Io isthe output current drawn by the load circuit.

FIG. 8A is a graph of simulation results representing the averagevoltage on the flying capacitor (Vf) and the output voltage (Vout)versus the duty cycle, corresponding to the circuits shown in FIGS.6A-B. The maximum output voltage is obtained when the duty cycle isequal to 0.5. When the duty cycle deviates from 0.5, Vf deviates from0.5 Vin, resulting in higher on-resistance for the MOSFETs, and hencethe output voltage starts to scale down below 0.5 Vin. Therefore, theoutput voltage is controlled through a duty cycle which controls theon-resistance of the switches. This technique simplifies the drivingscheme of the switches in the switched capacitor converters and allowsfor the use of a constant gate voltage to drive the floating switcheswhich are not connected to either Vin or ground nodes such as switchesS2 and S3. This technique allows also for the use of the duty cycle asthe main controlling parameter for the output voltage instead of theswitching frequency used in normal switched capacitor circuits which isa lossy regulation scheme.

FIG. 8B is a graph of simulation results representing the averagevoltage on the flying capacitor versus the duty cycle of the waveformscontrolling the switches for an input voltage equal to 1V for differentvalues of inductor size, according to an embodiment of the invention.The relation is plotted for different values for the inductor L in FIG.6A-B. The flying capacitor is balanced at 0.5 V (i.e., 0.5 Vin) when theduty cycle is equal to 0.5. The voltage on the flying capacitor startsdeviating from 0.5 Vin once the duty cycle deviates from 0.5. Thisoccurs due to the existence of an inductor L between the outputcapacitor (Co) and the flying Capacitor (Cf) as shown in FIG. 7A andFIG. 7B, which allows the voltage on the flying capacitor (Vf) todeviate from 0.5 Vin if its charging and discharging time are not equal.In this case, the voltage on the flying capacitor (Vf) can be adjustedby changing the duty cycle of the waveforms used to drive the fourswitches and becomes a function in the duty cycle. The dependency of theflying capacitor voltage on the duty cycle increases as the inductancevalue increases as shown in FIG. 8B.

The flying capacitor voltage (Vf) determines the overdrive voltage (Vov)of the turned on switches in each phase and hence their on-resistance.For example, the overdrive voltage (Vov) for switch S3 in the firstphase in FIG. 6A is a function in the flying capacitor voltage (Vf) andis given by Vov=Vgs−Vth=Vd−Vin+Vf−Vth, where Vth is the thresholdvoltage of the MOSFET. Accordingly, the on-resistance of the MOSFET S3is given by:

$R_{on} = {\frac{1}{{K( {W/L} )}( {V_{gs} - V_{th}} )} = {\frac{1}{{K( {W/L} )}( {V_{d} - V_{in} + V_{f} - V_{th}} )} = {f( V_{f} )}}}$where K is a constant related to the MOSFET technology and W and L arethe width and the length of the MOSFET, respectively. The same appliesfor the switch S2 in the second phase in FIG. 6B. Since the flyingcapacitor voltage (Vf) is a function in the duty cycle value (D), asillustrated in FIG. 8A and FIG. 8B, the on-resistance of the MOSFETsbecomes a function in the duty cycle as well. Therefore, theon-resistance of the MOSFETs is modulated using a duty cycle value.

FIG. 9 is a schematic circuit diagram illustrating an example of a4-level 4-state voltage regulator device with a switched capacitorcircuit capable of providing four different voltage levels connected toa low pass filter, according to an embodiment of the invention. Theconventional triple-ratio SCC topology (or series-parallel topology)known in the art may be selected as a SCC to build a multilevelmultistate voltage regulator device where all guidelines and techniquesintroduced previously are applied. The resulting regulator is a 4-level4-state voltage regulator.

This 4-level 4-state hybrid voltage regulator includes a switchedcapacitor circuit capable of providing four voltage levels (Vin, 0.67Vin, 0.33 Vin, 0) by using different configuration for the switches. Theswitched capacitor circuit is followed by a low pass filter. In thisspecific illustrative embodiment, the maximum number of states for anyconversion ratio to be able to provide a stable output voltage is two.The operation region is determined based on the two voltage levels wherethe desired output voltage point lies in between. The switched capacitorcircuit switches between these two voltage levels periodically and theduration of each voltage level is used to regulate the output voltage.In order to reduce the number of switching MOSFETs and to increase theeffective switching frequency, the phases of the different voltagelevels are interleaved under conditions and guidelines outlined in FIG.5. The maximum voltage drop on the inductor is limited to one third ofthe input voltage allowing for a smaller inductor size. Moreover, usingthe pre-mentioned method, the total number of switching MOSFETs per onecycle is reduced roughly by half compared to the conventional circuitallowing for lower switching losses which can be seen as an increase inthe effective switching frequency.

The 4-level 4-state voltage regulator of FIG. 9 has a series-parallelSCC topology followed by a LPF. The SCC has two flying caps (C1 and C2)and nine switches (S1, . . . , S9) and is capable of providing fourvoltage levels at its output. These four voltage levels are the inputvoltage Vin, two third the input voltage (⅔)Vin, one third the inputvoltage (⅓)Vin and the ground. The Vin voltage level is provided by adirect connection between the input node Vin and switching node Vx,where no flying caps are involved in the charge transferring process.This direct connection can be achieved by enabling switches S1 and S2 orenabling switches S5 and S6 or enabling both.

The (⅔) Vin voltage level is provided by two phases from the SCC wherethe two flying capacitors are involved in the charge transferringprocess. In the first phase, switches S1, S3, S5 and S7 are enabledresulting in the two flying capacitors connected in parallel and beingcharged through the input source. In the second phase, switches S2, S8and S9 are enabled resulting in the two flying capacitors connected inseries and being discharged through the inductor (L). The relativeduration between the two phases providing the (⅔) Vin are adjusted sothat the two flying capacitors (C1 and C2) are balanced at one third theinput voltage Vin. The optimum value in this case is found to be thatthe duration of the first phase in which C1 and C2 are charging isdouble the duration of the second phase in which C1 and C2 aredischarging.

The (⅓)Vin voltage level is provided by two phases from the SCC wherethe two flying capacitors (C1 and C2) are involved in the chargetransferring process. In the first phase, switches S1, S7 and S9 areenabled resulting in the two flying capacitors connected in series andbeing charged through the input source. In the second phase, switchesS2, S4, S6 and S8 are enabled resulting in the two flying capacitorsconnected in parallel and being discharged through the inductor (L). Therelative duration between the two phases providing the (⅓)Vin areadjusted so that the two flying capacitors (C1 and C2) are balanced atone third the input voltage Vin. The optimum value in this case is foundto be that the duration of the first phase in which C1 and C2 arecharging is half the duration of the second phase in which C1 and C2 aredischarging.

The ground voltage level is provided by a direct connection betweenground node and switching node Vx of the SCC where no flying capacitorsare involved in the charge transferring process. This direct connectioncan be achieved by enabling switches S4 and S3 or enabling switches S7and S8 or enabling both.

FIG. 10 is a table illustrating the three different operation regions ofthe 4-level 4-state voltage regulator device after applying the phaseinterleaving method, according to an embodiment of the invention. Ineach of the three operation regions, the operation timeline of thecircuit is divided into four time slots (i.e., states) T1, T2, T3 andT4. The odd time slots (T1 and T3) are assigned to phases of the firstvoltage level while the even time slots (T2 and T4) are assigned tophases of the second voltage level based on the general operationtimeline illustrated in FIG. 4B.

In the first operation region, the SCC is configured to periodicallyswitch its output between Vin and (⅔)Vin. In the second operationregion, the SCC is configured to periodically switch its output between(⅔)Vin and (⅓)Vin. In the third operation region, the SCC is configuredto periodically switch its output between (⅓)Vin and zero. The properoperation region is selected based on the desired output voltage asshown in the table of FIG. 10.

The table of FIG. 10 gives an indication of the switching lossesassociated with the switching behavior of the MOSFETs in the 4-level4-state voltage regulator. Inside each operation region, when going fromone phase to the next, some switches change their status from ON to OFFor vice versa, some remain ON and some remain OFF. The right arrows inthe table indicate a switch changing its status when going from onephase to the next. Having a SCC changing its output voltage periodicallybetween two voltage levels along with the interleaving between thephases of these two voltage levels result in reduced switching losses ofthe regulator. It can be noted from FIG. 10 that not all the switches ofthe SCC change their status when going from one phase to the next. Incontrast, FIG. 11 is a table illustrating the different operationregions of a conventional triple-ratio SCC known in the art.

From a comparison of FIGS. 10 and 11, it is seen that, on the one hand,during a full cycle in the first operation region of the 4-level 4-statevoltage regulator of the present invention (FIG. 10) there are 14switches changing their status (i.e., number of right arrows in firstoperation region). On the other hand, the number of switches changingtheir status during a full cycle of the conventional triple-ratio SCCoperating at (⅔)Vin voltage level (FIG. 11) is 28 (number of rightarrows in Vo=0.67 Vin region). Therefore, the 4-level 4-state voltageregulator of the present invention can result in lower switching losses.

FIGS. 12A-C are timing diagrams showing different configurations of aswitched capacitor circuit and the resulting voltage waveform in thefirst, second, and third operation regions of the 4-level 4-statevoltage regulator, according to an embodiment of the invention. In thefirst operation region (FIG. 12A), the two phases of the Vin voltagelevel are interleaved with the two phases of the (⅔)Vin voltage level(i.e., the odd time slots are assigned to phases of Vin voltage levelwhile the even time slots are assigned to phases of (⅔)Vin voltagelevel). The correspondent timeline of the first operation region isshown in FIG. 12A along with the resulting Vx waveform at the SCCoutput. The equivalent circuit of the SCC in each time slot is alsoshown. The total duration of the Vin voltage level during a fullswitching cycle (Tsw) is equal to DTsw while the total duration of the(⅔)Vin voltage level is equal to (1−D)Tsw. By adjusting the duty cyclevalue (D), a fine tuning of the output voltage value inside thatoperation region can be achieved. The output voltage (Vout) in this caseis given by Vout=(⅔)Vin+D(⅓)Vin. The relative duration between the twophases of the (⅔)Vin voltage level is kept at the optimum valuedescribed previously (i.e., the duration of the first phase is doublethe duration of the second phase) in order to maintain the voltage onthe two flying capacitors balanced at (⅓)Vin during the operation of theregulator.

In the second operation region (FIG. 12B), the two phases of the (⅔)Vinvoltage level are interleaved with the two phases of the (⅓)Vin voltagelevel (i.e., the odd time slots are assigned to phases of (⅔)Vin voltagelevel while the even time slots are assigned to phases of (⅓)Vin voltagelevel). The correspondent timeline of the second operation region isshown in FIG. 12B along with the resulting Vx waveform at the SCCoutput. The equivalent circuit of the SCC in each time slot is alsoshown. The total duration of the (⅔)Vin voltage level during a fullswitching cycle (Tsw) is equal to DTsw while the total duration of the(⅓)Vin voltage level is equal to (1−D)Tsw. By adjusting the duty cyclevalue (D), a fine tuning of the output voltage value inside thatoperation region can be achieved. The output voltage (Vout) in this caseis given by Vout=(⅓)Vin+D(⅓)Vin. The relative duration between the twophases of the (⅔)Vin voltage level is kept at the optimum valuedescribed previously (i.e., the duration of the first phase is doublethe duration of the second phase) to maintain the voltage on the twoflying capacitors balanced at (⅓)Vin during the operation of theregulator. Similarly, the relative duration between the two phases ofthe (⅓)Vin voltage level is kept at the optimum value describedpreviously (i.e., the duration of the first phase is half the durationof the second phase).

In the third operation region (FIG. 12C), the two phases of the (⅓)Vinvoltage level are interleaved with the two phases of the ground voltagelevel (i.e., the odd time slots are assigned to phases of (⅓)Vin voltagelevel while the even time slots are assigned to phases of ground voltagelevel). The correspondent timeline of the third operation region isshown in FIG. 12C along with the resulting Vx waveform at the SCCoutput. The equivalent circuit of the SCC in each time slot is alsoshown. The total duration of the (⅓)Vin voltage level during a fullswitching cycle (Tsw) is equal to DTsw while the total duration of theground voltage level is equal to (1−D)Tsw. By adjusting the duty cyclevalue (D), a fine tuning of the output voltage value inside thatoperation region can be achieved. The output voltage (Vout) in this caseis given by Vout=D(⅓)Vin. The relative duration between the two phasesof the (⅓)Vin voltage level is kept at the optimum value describedpreviously (i.e., the duration of the first phase is half the durationof the second phase) to maintain the voltage on the two flyingcapacitors balanced at (⅓)Vin during the operation of the regulator.

FIG. 13 is a graph of efficiency vs. output voltage showing a comparisonbetween 4-level 4-state voltage regulator and a conventionaltriple-ratio resonant switched capacitor regulator, according to anembodiment of the invention. Both converters are implemented on astandard CMOS technology with an input voltage of 1.2 V. The 4-level4-state device has higher efficiency than the conventional triple-ratioSCC. More specifically, the 4-level 4-state voltage regulator efficiencydoes not degrade quickly as the output voltage scales down, due to theefficient regulation scheme that is based on the pulse width modulationinstead of the frequency modulation used in the conventional switchedcapacitor converters which is a lossy regulation scheme. Moreover, thephase interleaving technique, applied in the 4-level 4-state voltageregulator, results in an increased effective switching frequency andreduced switching losses as discussed previously.

FIG. 14 is a graph of output ripples vs. output voltage showing acomparison between 4-level 4-state voltage regulator and a conventionaltriple-ratio resonant switched capacitor regulator in terms of outputvoltage ripples, according to an embodiment of the invention. The outputripples of the conventional triple-ratio topology increasessubstantially once deviating from the three normal operating points. Onthe other hand, the output ripples of the 4-level 4-state voltageregulator are kept low during most of the output voltage range.

FIG. 15 is schematic circuit diagram illustrating an illustrativeembodiment of a 5-level 8-state voltage regulator device with a switchedcapacitor circuit capable of providing five voltage levels connected toa low pass filter, according to an embodiment of the invention. This5-level 8-state hybrid voltage regulator has a SCC topology followed bya LPF. The SCC has two flying capacitors (Cf1 and Cf2) and eightswitches (S1, . . . , S8). It is capable of providing five voltagelevels at its output. These five voltage levels are Vin, 0.75 Vin, 0.5Vin, 0.25 Vin, and the ground voltage levels. Each of these voltagelevels can be provided by one or more different configurations ofswitches shown in the table in FIG. 16. Each configuration results in acertain connection between the two flying capacitors, input (or ground)node and Vx node where each of the two flying capacitors is eithercharging (up-arrow), discharging (down-arrow) or idle (i.e. floating) asindicated in the table in FIG. 16. It can be noted that the “Vin” andground voltage levels are provided by direct connection between powersupply rails and Vx node. The maximum number of phases to provide any ofthe five voltage levels is four, therefore a one switching cycle isdivided into eight time slots (i.e., states). The average voltages onthe flying capacitors Cf1 and Cf2 during normal operation of the circuitare 0.5V in and 0.25 Vin, respectively. This can be proved by solvingthe KVL equations of the configurations providing each of the fivevoltage levels. By following the guidelines and the conditions mentionedin FIG. 5, the flying capacitors are balanced at 0.5 Vin and 0.25 Vin,respectively, as the SCC goes from one state to another.

FIG. 16 is a table illustrating the different operation regions of the5-level 8-state voltage regulator device using a phases interleavingmethod, according to an embodiment of the invention. There are fourdifferent operation regions depending on where the desired outputvoltage (Vo) lies. In the first operation region, the SCC is changingits configuration periodically so that the Vx waveform at the output ofthe SCC is switching between Vin and 0.75 Vin. Similarly, the Vxwaveform switches its voltage level periodically between the two voltagelevels of each operation region. Selecting the required operation regionis considered a coarse tuning of the output voltage Vo. Fine tuning ofoutput voltage value Vo inside each operation region is done bycontrolling the relative duration between the two voltage levels of theVx waveform through the adjustment of a duty cycle value.

In each of the four operation regions, the operation timeline of thecircuit is divided into eight time slots (i.e., states) T1, . . . , T8.The odd time slots T1, T3, T5, T7 are assigned to phases of the firstvoltage level while the even time slots T2, T4, T6, T8 are assigned tophases of the second voltage level based on the general operationtimeline illustrated in FIG. 4B. The durations of the even and odd timeslots are given by T1=T3=T5=T7=0.25 DTsw, T2=T4=T6=T8=0.25(1−D)Tsw,T1+T2+T3+T4+T5+T6+T7+T8=Tsw, where D is the duty cycle and Tsw is theduration of one switching cycle. The table in FIG. 16 gives a summary ofthe circuit operation showing switch configurations assigned todifferent time slots of a switching cycle inside each operation region.The switch configurations are assigned in a way that ensures the circuitfunctionality and satisfies the guidelines of FIG. 5.

FIG. 17A-B show simulation result from a 5-level 8-state voltageregulator circuit in FIG. 15 built on a standard CMOS technology with aninput voltage of 1V.

FIG. 17A is a graph of the voltage on the flying capacitors vs. time,showing the voltage Vf1 on the flying capacitor Cf1 and the voltage Vf2on the flying capacitor Cf2 in the circuit of FIG. 15 when the voltageregulator is operated at the first operation region with the sequenceshown in the table in FIG. 16 and with a duty cycle of half. The averagevoltage Vf1 on the flying capacitor is roughly balanced at 0.5 V (i.e.,0.5 Vin) while the average voltage on the flying capacitor Cf2 isroughly kept balanced at 0.25 V (i.e., 0.25 Vin).

FIG. 17B is graph of simulation results representing the voltage Vout atthe device output node vs. time (top) and the voltage Vx at the SCCswitching output node vs. time (bottom), for the 5-level 8-state voltageregulator circuit shown in FIG. 15 when the regulator is operated in thefirst operation region with the sequence shown in the table in FIG. 16and with a duty cycle of half. The Vx node is switching its voltagelevel periodically between 1 V (i.e., Vin) and 0.75 V (i.e., 0.75 Vin)at a switching frequency which is four times the frequency of one cycle(which is equal to 1/Tsw where Tsw is the total duration of the eighttime slots as explained previously). The Vin voltage level and the 0.75Vin voltage level the Vx waveform is switching between represents thefirst and the second voltage levels of the first operation regiondescribed in the table in FIG. 16. The theoretical output voltage valueof the converter operating in the first operation region and with a dutycycle of half is Vout=0.75 Vin+0.25 VinD=0.75 Vin+0.125 Vin=0.875 Vin,which is equal to 0.875 V for an input voltage of 1 V. However, theoutput voltage value shown in FIG. 17B is slightly lower than 0.875 Vdue to the losses exhibited in the regulator circuit.

FIG. 18 is a schematic circuit diagram illustrating the structure of acontroller unit and its working principle, according to an embodiment ofthe invention. The control unit is capable of providing different switchdriving waveforms to control the operation of a switched capacitorcircuit having multiple phases and regulate the output voltage. A statemachine device with a lookup table determines the configuration of eachswitch in a certain phase and switches between these configurations whengoing from one phase to another. The controller is capable ofdetermining the operation region as well.

As detailed in FIG. 18, the digital controller is used to control avoltage regulator device that has a SCC with n switches as one of itsparts. The voltage regulator device is capable of operating at differentoperation regions according to the desired output voltage. Each of theseoperation regions has multiple states. In each of these states, thestatus of each switch in the SCC is either ON or OFF. The digitalcontrol unit takes the desired reference voltage 1806, current inputvoltage 1808 to the regulator and current output voltage 1804 from theregulator as inputs and generates n control signals for the switches S1,S2, . . . Sn in the SCC.

The controller unit has a clock generator 1802 is used to generate themain clock signal of the system with a period equal to one over theswitching frequency of the regulator (Fsw). A normal compensator block1810 is used to adjust the dynamic response of the regulator by takingas an input the desired reference voltage value 1806 and the currentoutput voltage value 1804 as an input and generates a duty cycle valueas an output.

A delay line 1800 is used to generate a pulse width modulated signalversion 1822 from the main clock signal. The delay line has a series ofcascaded tapped buffers followed by multiplexers and flip flops. Thedelay line block takes the main system clock and the duty cycle value asan input and generates a pulse width modulated signal 1822 as an output.The high portion of the modulated signal represents the duration of onestate of the SCC while the low portion of the modulated signalrepresents the duration of the following state.

The pulse width modulated signal and its inverse go as input to nmultiplexers (1816, 1818, . . . 1820) where n is the number of theswitches to be controlled in the SCC circuit. Each of the n multiplexershas two additional inputs corresponding to the logic high “1” and thelogic low “0” signals. The proper operation region is determined by theoperation region determination block 1812 based on the input voltagevalue 1808 and the desired reference voltage 1806. The output of thisblock goes as an input to a state machine 1814 that stores informationabout the different states of the regulator inside each operation regionand has information about the status of the n switches inside each stateof that operation region.

The state machine 1814 generates n control signals that work as theselection input for the n multiplexers. According to the status of eachswitch, one of the four inputs to the multiplexers is selected. If theswitch is on in the first state and is off in the next phase, then thepulse width modulated signal is selected. If the switch is off in thefirst phase while it is on in the next phase then the inverted pulsewidth modulated signal is selected. If the switch is always on duringthe two states then the logic high (i.e. “1”) is selected. If the switchis always off in the two states then the logic low “0” is selected.

The state machine 1814 has an internal counter that counts from zerountil (m−1) for an operation region that consists of 2 m states. Thecounter and the state machine are triggered at the positive edge of themain system clock generated from 1802. Therefore, the n outputs of thestate machine are updated at the positive edge of the main system clock.Once the counter reaches to (m−1) when counting, which means a fullswitching cycle of 2 m states is provided, the controller is reset andstarts counting again from zero. This process is repeated along theoperation timeline of the regulator.

The invention claimed is:
 1. A voltage regulator device, comprising: aswitched capacitor circuit (SCC) comprising capacitors and switches,wherein the SCC is configured to receive an input voltage and produce atan output n different voltage levels (V1, V2, . . . , Vn) periodicallywith a period equal to one over a switching frequency of the voltageregulator device; a low pass filter (LPF) directly connected to the SCC,the LPF comprising an inductor and a capacitor, wherein the LPF receivesthe output of the SCC at an input and produces a regulated outputvoltage at an output; and a control unit configured to receive a targetreference voltage and a current output voltage as an input and producedriving waveforms to the switches of the SCC; wherein a one switchingcycle of operation is divided into multiple time slots wherein even timeslots are assigned to phases of a first conversion ratio and oddtimeslots are assigned to phases of a second conversion ratio.
 2. Thedevice of claim 1, wherein the control unit is configured to control theSCC to produce the n voltage levels (V1, V2, . . . , Vn) with differentdurations.
 3. The device of claim 1, wherein the control unit isconfigured to control the SCC to change a duty cycle.
 4. The device ofclaim 1, wherein the SCC is configured to produce the n differentvoltage levels (V1, V2, . . . , Vn) such that all the n differentvoltage levels (V1, V2, . . . , Vn) are higher than or equal to theinput voltage to form a step-up regulator.
 5. The device of claim 1,wherein the control unit is configured to control the SCC by controllinga relative duration between different phases to adjust an average steadystate voltage on each flying capacitor in each conversion ratio of theSCC.
 6. The device of claim 1, wherein the control unit is configured tocontrol the SCC to operate on a conversion ratio having multiple phaseswith phase durations.
 7. The device of claim 1, wherein switches in theSCC are resistance modulated by controlling a flying capacitor averagevoltage to alter an overdrive voltage of the switches.
 8. The device ofclaim 1, wherein the SCC consists of two flying capacitors and nineswitches.
 9. The device of claim 1, wherein the SCC operates at fourdifferent conversion ratios to provide four equally spaced voltagelevels at its output.
 10. The device of claim 1, wherein the controlunit is configured to control the SCC to switch its configurationperiodically between a first conversion ratio and a second conversionratio to produce a desired output voltage.
 11. The device of claim 1,wherein the SCC consists of two flying capacitors and eight switches.12. The device of claim 1, comprising a decision circuit to decide anoperation region based on a required reference output voltage and theinput voltage.
 13. The device of claim 1, comprising a state machineconfigured to receive an operation region as an input and produce noutputs determining states of n driving waveforms using a look up table.14. The device of claim 1, wherein the SCC is configured to produce then different voltage levels (V1, V2, . . . , Vn) such that all the ndifferent voltage levels (V1, V2, . . . , Vn) are lower than or equal tothe input voltage to form a step-down regulator.
 15. The device of claim1, wherein the SCC is configured to produce the n different voltagelevels (V1, V2, . . . , Vn) such that some of the n different voltagelevels (V1, V2, . . . , Vn) are higher than the input voltage and someof the n different voltage levels (V1, V2, . . . , Vn) lower than theinput voltage to form a step-up/down regulator.
 16. A voltage regulatordevice, comprising: a switched capacitor circuit (SCC) comprisingcapacitors and switches, wherein the SCC is configured to receive aninput voltage and produce at an output n different voltage levels (V1,V2, . . . , Vn) periodically with a period equal to one over a switchingfrequency of the voltage regulator device; a low pass filter (LPF)directly connected to the SCC, the LPF comprising an inductor and acapacitor, wherein the LPF receives the output of the SCC at an inputand produces a regulated output voltage at an output; and a control unitconfigured to receive a target reference voltage and a current outputvoltage as an input and produce driving waveforms to the switches of theSCC; wherein a one switching cycle of operation is divided into fourtime slots wherein even time slots are assigned to phases of a firstconversion ratio and odd timeslots are assigned to phases of a secondconversion ratio.